Purpose:
Recent advances in optical coherence tomography allow visualization of the details of the optic nerve structure and substantially increase the understanding of the pathology of optic nerve disease. However, the infrared light source is limited in its ability to analyze the retrobulbar structure because of insufficient penetration; in contrast, X-rays can penetrate deeper. We developed a model for retrobulbar angiography with computed tomography (CT) to reveal the retrobulbar structures around the optic nerve head.

Methods:
After general anesthesia was induced in 4-week-old SD rats, under airway control, we exposed the common carotid artery and internal and external carotid arteries (ICA/ECA). After ECA blockage, an arterial catheter was inserted into the ICA. After closing wound, the rats were observed alive with CT (R_mCT2, Rigaku Corp.). Under a monitor, we injected a contrast agent, iohexol (Omnipaque, Daiichi-Sankyo) through the catheter. An iodine-containing polymer solution also was injected (3.5x108 polymers (R=15 μm)/SDS 0.05% Solution, Sekisui Plastics Co.), after contrast agent washout. The CT values (HU) were recorded through R_mCT2 at baseline(A), maximal contrast agent enhancement (B), washout (C), and maximal iodine-containing polymer enhancement (D). The results were analyzed (Compare Analysis, Rigaku Corp.).

Results:
The local area governed by the ICA was stained only in rats with a closed ECA. The orbit CT value (oCTv) was 740.71±10.05 at B, which was much higher than -51.62±1.58 at A (P<0.01). The oCTv was 209.82±19.90 at D, which was similar to 229.28±18.51 at C (P=0.31). The maximal enhanced oCTv was 313.60±62.04, which was higher than that during polymer injection (90.72±1.42) (P<0.05). The maximal enhanced CT values of the eye were 143.39±29.40 and 192.27±66.76 with polymer (P=0.20).

Conclusions:
We localized the area governed by ICA by enhancement; the CT value of the orbit had increased contrast after enhancement and decreased after washout. The polymer stayed in the eye after the contrast was flushed from the orbit. We developed a model for retrobulbar angiography that makes it easy to adjust the condition for obtaining images.